Studies on the structure of macromolecules in cancer cells are essential for defining the biochemical lesion(s) distinguishing cancer cells from normal cells. Since there is ample evidence, mainly from chromatographic studies, for alterations of tRNAPhe in cancer cells but almost no informatiin is available on sequences of tumor tRNAs we propose to determine by novel sensitive radioactive derivative methods for structural analysis of RNA developed in our laboratory. We plan to concentrate initially on the structural characterization of tRNAPhe from human placenta and, at a later stage, to sequence tRNAPhe species from tumors. The radioactive derivative methods for sequencing of RNA have been designed in such a way that no in vitro labeling is required and only small amounts of tissue are needed. They are thus particularly suited for structural investigation on human tumor RNAs. The sequencing scheme is based on complete and partial enzymic degradation of the RNA to oligonucleotides, thin-layer separation of the digests on PEI-cellulose, isolation of oligonucleotides from the chromatograms, nuclease digestion of the oligonucleotides, radioactive labeling of the degradation products, and chromatographic analysis of the labeled derivatives.